1. Field of the Invention
The present invention relates generally to the separation of solid particles that are entrained in a gaseous process fluid maintained at an elevated pressure and, more particularly, relates to the separation of wood fibers entrained in process generated steam in order to reduce the amount of volatile organic compound (VOC) emissions generated in the refining of wood fiber for the manufacture of medium density fiberboard (MDF).
2. Description of the Prior Art
It is well known in the art to use a pressurized cyclone in thermo-mechanical pulping (TMP) for the separation of wood fibers from a gaseous process fluid, typically steam. The steam which is separated from the wood fibers is then often recovered for reuse in the pulping process. Examples of such pressurized cyclones are disclosed in U.S. Pat. Nos. 4,555,254 and 4,725,295, both of which are incorporated herein by reference.
In a system for manufacturing medium density fiberboard (MDF), the operating parameters are somewhat different than in a TMP system. Moreover, the system pressure is generally higher and less steam or gaseous process fluid is produced. Accordingly, experience has proven that there is insufficient steam in MDF refining to justify steam recovery for reuse within the process. Additionally, the use of traditional pressurized cyclones within conventional MDF processes has often resulted in the wood fibers congealing, or clumping together, and thereby preventing the exhaust of the separated wood fibers from the cyclone. As such, the wood fibers will often combine to form a single mass thereby preventing proper operation of the cyclone.
Therefore, while the use of pressurized cyclones in traditional MDF processes has typically been avoided, the present applicants have further investigated the use of such pressurized cyclones for the purpose of reducing volatile organic compound (VOC) emissions. Moreover, VOC emissions are traditionally generated in the refining of wood chips, sawdust and wood fibers during the manufacture of MDF. More particularly, VOCs, such as turpene, contained within the process steam are typically released when the wood fiber is dried in a conventional dryer. Applicants have realized that by reducing the amount of steam conveyed to the dryer with the wood fibers, VOC emissions may be reduced. Moreover, VOCs contained within steam separated from the fibers may be oxidized in a boiler to produce carbon dioxide and water vapor.
Additionally, the wood fibers, stripped of the excess conveying steam by the pressurized cyclone, are then accessible for more efficient resin addition. Further, the load applied to the dryer is significantly reduced.
Accordingly, there is a need for a pressurized cyclone which may be effectively used within the MDF process. Moreover, there is a need for such a pressurized cyclone which efficiently separates steam from the entrained wood fibers while preventing the undesired congealing, or clumping, of the wood fibers and the resultant plugging of the pressurized cyclone outlet.
The present invention provides a cyclone for use in a pressurized materials processing system, such as a medium density fiberboard (MDF) processing system, for separating solid material which is entrained in a gaseous fluid.
Moreover, the present invention relates to a cyclone for receiving a fluid flow in which solid material is entrained in a gaseous fluid maintained at an elevated pressure, the cyclone including a housing having an upper end, a lower end and a substantially cylindrical side wall defining a longitudinal axis. An inlet is formed within the housing proximate the upper end and is tangentially oriented relative to the side wall for inducing the fluid flow to rotate about the longitudinal axis, thereby imparting centrifugal force on the solid material. A gaseous fluid outlet extends upwardly from the upper end of the housing for providing egress of a first, or separated, portion of the gaseous fluid. An entrained solid outlet is formed within the housing and positioned proximate the lower end for providing egress of the solid material entrained within a second, or conveying, portion of the gaseous fluid.
An agitator assembly is positioned within the housing proximate the lower end. The agitator assembly includes a vertically extending, rotatably supported drive shaft coaxially disposed with the longitudinal axis. A plurality of agitator members are supported for rotation with the drive shaft about the longitudinal axis, each of the plurality of agitator members including opposing first and second ends and extending radially outwardly toward the side wall. The first end of each agitator member is supported by a hub fixed to the drive shaft while the second end of each agitator member is positioned proximate the side wall.
A plurality of anti-rotation members are removably supported by the side wall in axially spaced relation to the plurality of agitator members. Each of the plurality of anti-rotation members includes opposing first and second ends and extends radially inwardly through one of a plurality of mounting apertures formed within the side wall of the housing. The first end of each anti-rotation member is supported outside the housing while the second end is positioned proximate the hub.
A motor is operably connected to the drive shaft for rotating the plurality of agitator members about the longitudinal axis, whereby the agitator members move relative to the anti-rotation members for agitating the solid material. The anti-rotation members prevent the solid material from forming a solid plug which moves in unison with the agitator members.
In operation, the gaseous fluid and entrained solid material enters the housing substantially tangential to the side wall, and is therefore forced to rotate or swirl about the longitudinal axis in the form of a vortex. The vortex results in centrifugal force causing the entrained solid particles to move outwardly toward the inner surface of the side wall and separate from the gaseous fluid. The first, or separated, portion of the gaseous fluid exhausts upwardly through the gaseous fluid outlet. The first portion of the gaseous fluid is then preferably sent to a boiler which oxidizes the volatile organic compounds contained therein through combustion. The entrained solid material along with the second, or conveying, portion of the gaseous fluid move downwardly to a lower portion of the housing.
The motor causes rotation of the drive shaft and the plurality of agitator members positioned proximate the lower end of the housing. The meshing interaction between the rotating agitator members and the stationary anti-rotation members prevent the congealing or clumping of the solid particles proximate the entrained solid outlet. As such, the second portion of the gaseous fluid conveys the solid material from the lower end of the housing through the entrained solid outlet to the next processing station, typically a dryer.
Therefore, it is an object of the present invention to provide a pressurized cyclone for reducing the amount of volatile organic compound emissions produced during medium density fiberboard processing.
It is a further object of the present invention to provide a pressurized cyclone for efficiently separating process generated gaseous fluid from entrained solid material.
It is another object of the present invention to provide a pressurized cyclone including an agitator assembly for preventing the plugging of the entrained solid outlet.
It is a further object of the present invention to provide such an agitator assembly having a simple and inexpensive design.
It is still yet another object of the present invention to provide such an agitator assembly which includes removably supported anti-rotation members for facilitating disassembly, cleaning and maintenance.
Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.